Someone seems to have found a solution to this: load a cab that is empty. In this cab collection here is a cab that is called "Cab-bypass". I did not check it out yet and don't know how it is done but this seems a good way to go.
Adding a 'blank' cab works very well indeed for power amp/cab use, and was essential in earlier firmware to get a consistent sound accross profiles. Recent firmware has really improved the cab off sound in the monitor section however so now I rarely even bother to load a blank cab any more.